1. Field of the Invention
The invention relates to the field of electromotive power systems. More particularly, the invention relates to the field of stepping motors. In still greater particularity, the invention relates to the field of stepping motor speed controls. By way of further characterization, but not by way of limitation thereto, the invention is a method for driving a stepping motor by regulating the pulse width of the drive pulses with a microprocessor.
2. Description of the Prior Art
Previously, a limitation in the use of stepping motors was its inability to run at high speeds. This limitation was due to motor winding inductance. That is, it takes time for the windings to be energized to their rated current. This lack of instantaneous response causes the motor to stall at higher frequencies.
There are several solutions in existence to solve the above described problem. One solution is to provide a constant current source for the motor instead of a constant voltage source. A second solution is to start off each step with a higher voltage across the winding and then drop to a standby voltage as soon as the motors' rated current is reached. This second approach has been widely adopted and a number of devices today incorporate this type of bi-level driving circuit. However, employing this kind of a bi-level drive causes the motor to run with excess vibration and resonance producing audible noise at lower frequencies because it is being driven unnecessarily hard. That is, the high voltage supplied initially causes instantaneous high torque which results in abrupt rotor displacement with overshoot and oscillation. It would be desirable to have a method for employing the bi-level driving circuit and yet avoiding the rough motor problem at low speeds.